Most everyday listening environments consist of a multitude of sounds, many of which are fluctuating in level over time. The way in which the brain sifts apart this acoustic complex into its constituent sound sources is referred to as auditory perceptual organization. The root interest of this project is in understanding the role of temporal processing in perceptual organization, and how aging and impaired auditory systems can compromise this ability. The focus of this project is on delineating the specific types of temporal processing deficits that emerge early in the aging process, and on differentiating these from deficits associated with advanced age and cochlear hearing loss. Three areas of temporal processing are investigated: (1) stimulus onsets and temporal fine structure; (2) temporal envelope coding; and (3) the relationship between temporal envelope processing and spectral integration in modulated maskers. The project utilizes both psychophysical and electrophysiological methodologies, and incorporates both speech and non-speech measures. The experiments test adults across a wide age range and include participants with normal hearing as well as hearing loss. Data will be analyzed using descriptive statistics, tests of correlation, and analyses of variance. The relevance of the project to public health is that it will lead to a clearer understanding of how the temporal features of sound are processed, and how changes in the auditory system due to age and hearing loss might affect these abilities. This research project is relevant to public health because it advances our understanding of how good hearing depends on the ability to process temporal features of sound. The project has direct application to hearing health because it is designed is to uncover how changes in the auditory system due to age and hearing loss affect the ability to process important temporal features.